This application seeks funding for the purchase of a scanning transmission electron microscope to be used for high-resolution morphological studies of diverse samples of biological interest. We will equip the microscope with an x-ray analysis device and a high-gain TV camera for quantitative measurement and high-resolution localization of elements of biological interest and low-irradiation dose imaging. No instrument with similar capabilities currently is available to the biomedical researchers at the Storrs campus of the University of Connecticut. The microscope will be installed in an established multi-user facility with an experienced staff and its continued support is assured by the University. PHS-supported projects of major users, which will account for more than 75% of the use of the new instrument, include studies of: 1) Ca regulation in striated muscle. The requested instrument will be used for electron probe x-ray microanalysis and high-resolution imaging of freeze-fracture replicas and hydrated and freeze-dried cryosections of rapidly frozen skeletal and cardiac muscle (Cantino). 2) Changes in cellular metabolism and structure during acetaminophen toxicity and recovery. The requested instrument will be used for ultrastructural and immunochemical studies in liver, kidney, and other organs (Cohan and Khairallah). 3) Identification and localization of growth guidance and adhesion factors in the outgrowth of peripheral nerves and formation of target tissue associations. The requested instrument will be used for ultrastructural and immunochemical studies. Analytical studies would also be undertaken as a new direction of investigation by these two (independent) investigators (Covault, Landmesser). 4) Regulation of development of Ca++ channels and regulation of axonal survival during development. The new instrument would be used for immunochemical and ultrastructural studies (Pilar). 5) Effects of heat shock on the structure and function of polarized monolayers of kidney epithelia. The new instrument would be used to correlate ultrastructure with physiological status. Localization of P and Ca using the analytical system will represent a new direction (Renfro). 6) Plasma membrane function using phospholipase probes. The requested instrument will be used for ultrastructural analysis to monitor membrane structure in preparations used for biochemical analysis. Further characterization of vesicles by analytical microscopy will be added (Rosenberg). 7) Initial steps in the morphogenesis of tobacco mosaic virus. The new microscope will provide capabilities necessary for studies of highly radiation-sensitive frozen hydrated samples at low electron dose (Schuster and Raghavendra).